It will vary. Depends on what type of food you are feeding, wether you need to account for things such as housing, feeders & waterers, wether you chose to use vitamins in their water, bedding..... just to name a few. Personally for me I had the cost of the bird ($2 a piece x8), plus $16 for food (I get 100lbs of food from the mill for $16), I already had the feeders and waterers, as well as the brooder and coop and run. I do spoil my chickens at times with treats so figure in about $20 for a seed/dry fruit/nut mixture that they love. I do not use vitamin in water so I didn't spend anything there. I use straw as bedding in the brroder and coop and I try to keep it clean so I would say $20 for 15 bales. You can also try to figure out cost of running brooder/heat lamp but I don't.
That should give you a little bit of an idea. Prices vary depending on where you live, what brand you buy, ect. I hope this helped you a little.